In certain devices comprising an illuminated display, a circuit is provided for measuring the ambient luminosity or ambient light level, and to automatically adjust the light intensity of the display according to the measured lighting level. This especially enables to improve the user-friendliness of the display and/or to save power.
Circuits for measuring the ambient luminosity level are known, which comprise a photodiode used in reverse mode, having its junction capacitance discharged by a photocurrent according to a received light intensity.
A disadvantage is that the provision of a photodiode specifically dedicated to measuring the ambient luminosity level increases the cost, the complexity, and the bulk of the device.